Weird Sound problem: Music can be heard but windows program's sounds cant...??

Hi,
I have a problem but unable to get it on right track........

I have no Windows Event sounds. Although, all other sounds are working, like playing music, movies etc. I changed the windows default sound scheme. But nothing helped. I checked the sound files in the Media folder, when i played them on Winamp they played. But when i try to play them in the sound scheme window, they dont......?
Sounds like Yahoo Buzz are too low at full volume but mp3 is blasting at that volume.
any advise?
thanks in advance.
TheHacker

Check your speakers are plugged into the green 3.5mm jack in the back of your pc and not the blue one